Vinyl resin coatings and process producing the same



?aienied May 30, 1939 g mam umrso STATES PATENT OFFICE I vnwn RESIN coa'ixz inn raocriss rao UCING SAME Arthur K. Doolittle, South Charleston, W. Va., assignor to Carbide and Carbon Chemicals Cor.-

poration, a corporation of New York Application December 12, 1936,

l lo Drawing.

Serial No. 115,531 6' Claims. 260-86) 1 type may be prepared from vinyl chloride and vinyl acetate in-reaction proportions of about 60 1 to 95 parts by weight of vinyl chloride to from about 40 to 5'pa'rts of the acetate. The preparation of the resins forms no part of the present 0 invention, and they are similar to those shown and described inPatent No. 1,935,577, issued to E. W. Reid on November 14, 1933. Within the broad class of such resins, those containing in the polymer fromiabout 80 to 90,parts by weight of the vinyl chloride are particularly suitable for the purpose of this invention.

.While the inherent quality of these vinyl resins,

especially their physical and chemical resistance, makes them excellently suited for surface coating purposes, their strong adhesion to metals and similar smooth surfaces has only been obtained with'eertain diiiiculties. It-has previously been found, for example, that adequate adhesion to metal'surfaces can, in most instances, only be provided by suitable baking of the applied coating. and that the best baking temperatures are above those at which the vinyl resin will normally begin to decompose without suitable precautions to prevent such action. To prevent or retard this decomposition, it has been considered necessary to incorporate with the resin'certain heat stabilizing materials which will permit proper baking without sumcient decomposition to adversely affect the adhesive and resistant qualities of the finish. 5 While stabilizers heretofore proposed have been operative under many conditions, and within certain limits, they have not shown a completely satisfactory protective function in coatings applied to surfaces of iron, tin-plate and zinc.

50 The present invention is also directly concerned with the heat stabilization of-these vinyl resin coating compositions, and the principal object thereof is to provides. more emcacious means and method of insuring thermal stability, with accom- 5 panying strong adherence and resistance, of vinyl incorporate in coating compositions, containing resin coatings and finishes baked on-iron, tinplate and zinc metal surfaces.

' The novelty in the invention is based primarily upon further discoveries which have been made concerning the nature of, and the conditions 5 affecting, thermal decomposition of vinyl resins.

I have found, for example, that inthe presence of, and in contact with, metals such as iron, tin-plate and zinc, the tendency toward decomposition of coatings containing these resins is more pro- 0 nounced than on surfaces of other materials, and it appears that such metals, or their reactive compounds promote or catalyze decomposition on baking. At the same time, it has further been determined that massive forms or thick films of vinyl resin compositions are noticeably more susceptible to thermal decomposition than relatively thin films ofthe type suitable for use in protective coatings, and deterioration through reaction within the resin mass appears to result at elevated temperatures regardless of the nature of the surface with which it is in contact.

It is therefore proposed by this invention to vinyl resins as the essential film-forming ingredient, stabilizing materials adapted essentially and primarily to protect the applied coating from deterioration through the catalyzing effect of iron, tin-plate, zinc, alloys containing substantial proportions of these metals, and other metal surfaces which similarly promote thermal decomposition. In producing a protective coating, decomposition through other causes is then substantially eliminated by exercising close control of the applied film thickness, which should not be greater than 0.01 inch, and preferably in the neighborhood of 0.005 inch.

Stabilizers suitable for this purpose include materials capable of preventing the acid decomposition products formed, when the resin coating is heated to 275 F., or higher, from contacting or reacting with the metal surface, including, for example, materials which will serveto set up a physical or chemical barrier between the harmful metallic surface and the coating film. The stabilizers preferred by this invention are materials which when applied to the metal as a component and will form on surfaces of iron and tin a proat tective coating resistant to further attack or reaction which may promote decomposition in the weight of vinyl chloride, has effected excellent stabilization of a resin coating on iron and tin, when the film thickness as applied is less than 0.01 inch. Other acidic compounds, such as phosphoric acid, phosphoric anhydride and thioglycollic acid have been found to function in a substantially similar manner.

With these stabilizers it is of importance in applying the coating to maintain a film thickness not greater than 0.01 inch-and preferably around 0.005 inch. This will avoid any resin decomposition which is normally encountered purely within the resin mass when heated in forms of larger dimensions. The actual proportion of stabilizer necessary to effect the best results will vary with the nature of the particular lacquer formula desired, as wellas with the temperature and time of baking and other conditions.v Normally a range of 5% to 15% by weight of the vinyl resin is suitable, with complete and thorough dispersion of the stabilizing material.

It will be understood that a variety'of solvents,

plasticizers, coloring materials and modifying agents may be present in lacquer formulas employing these stabilizers. The compositions of the invention are especially useful as priming coats, although they are not limited to this application, and the film stability is still maintained, for example, when applied over undercoats containing pigments composed of iron or zinc metal compounds.

Modifications other than as disclosed will be apparent to those skilled in the art, and are intended to be included within the scope of this invention as defined in the appended claims.

I claim:

l. A vinyl resin composition for coating metal surfaces of iron and tin-plate, comprising as the essential film-forming ingredient, a resin resulting from the conjoint polymerization of vinyl chloride and vinyl acetate, together with a stabilizer material comprising a member of the group consisting of acid phosphates and sulfides, said stabilizer being adapted to react with the metal surface to form a film thereon which is non-reactive with thermal decomposition products of said resin.

2. A vinyl resin composition for coating metal surfaces of iron and tin-plate, comprising as the essential film-forming ingredient a resin resulting from the conjoint polymerization of vinyl chloride and vinyl acetate and containing about 80% to 90% vinyl chloride in the polymer, together with a stabilizer material comprising about 5% to 15% by weight ofthe resin of amember of the group consisting of acid phosphates and sulfides, said stabilizer being adapted to react with the metal surface to form a film thereon which is non-reactive with thermal decomposition products of said resin.

3. A vinyl resin composition for coating metals of iron and tin-plate, comprising as the essential film-forming ingredient a resin resulting from the conjoint polymerization of vinyl chloride and vinylacetate and containing about 80% to 90% of vinyl chloride in the polymer, together with about 5% to about 15% of calcium dihydrogen phosphate intimately dispersed throughout said coating composition.

4. Process for producing strongly adherent and resistant surface coatings on metals of iron and tin-plate, which. comprises forming on said metal surface in a filmthickness less than 0.01inch a coating containing as the essential film-forming ingredient a vinyl resin formed by the conjoint polymerization of vinyl acetate and vinyl chloride, said vinyl resin having intimately incorporated therewith a stabilizing material which reacts with the metal surface to form a film thereon which is non-reactive with thermal decomposition products of said resin and comprising a member of the group consisting of acid phosphates and sulfides, and subsequently baking said coating at a temperature above 275'F.

5. Process for producing strongly adherent and resistantsurface coatings on metals of iron and tin-plate, which comprises forming on said metal surface in a film thickness of about 0.005 inch a coating containing as the essential film-forming ingredient a vinyl resin formed by the conjoint polymerization of vinyl chloride and vinyl acetate and containing about 80% to 90% vinyl chloride in the polymer, said vinyl resin having intimately'incorporated therewith about 5% to about 15% of calcium dihydrogen phosphate, and subsequently baking said coating at a temperature above 300 6. A vinyl resin composition for coating metal surfaces of iron, tin-plate and zinc, comprising as the essential film-forming ingredient a resin substantially identical with'that formed by the conjoint polymerization of a vinyl halide and a vinyl ester of an aliphaticacid, together with at least one stabilizer material of-the group consisting of acid phosphates and sulfides, said stabilizer being adapted to'react with the metal surface to form a film thereonwhich is non-reactive with thermal decomposition products of said resin. 

